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J. Virol., 12 1997, 9016-9023, Vol 71, No. 12
K Falk, E Namork, E Rimstad, S Mjaaland and BH Dannevig
Infectious salmon anemia (ISA) virus is the cause of infectious salmon
anemia in farmed Atlantic salmon. The virus has been shown to contain RNA
with structural characteristics similar to those of accepted members of the
Orthomyxoviridae. Further biochemical, physiochemical, and morphological
characterization of ISA virus was undertaken to clarify its taxonomic
position. The virus was found to be sensitive to chloroform, heat, and low
pH and agglutinated erythrocytes from fish. Erythrocytes from mammals or
birds were not agglutinated. Receptor- destroying enzyme activity was
detected, and the nature of this enzyme was suggested to be an
acetylesterase. The buoyant density of the virus was 1.18 g/ml in sucrose
and CsCl gradients. The maximum rate of virus replication was observed at
15 degrees C, while no virus was produced at 25 degrees C. Actinomycin D
inhibited viral replication, and viral antigen was detected in nuclei by
immunofluorescence. The addition of trypsin to the culture medium during
virus replication had a beneficial effect on virus replication. ISA virus
contains four major polypeptides with estimated molecular sizes of 71, 53,
43, and 24 kDa. Electron microscopy revealed structures closely resembling
the nucleocapsids of influenza virus. Mushroom-shaped surface projections
were a distinctive morphological feature, which differed from the
rod-shaped hemagglutinin projections of the influenza viruses. The data
reported here support the relationship of ISA virus to the
Orthomyxoviridae, although ISA virus differs from influenza viruses in some
morphological characteristics and in showing restricted hemagglutination,
in different specificity of the receptor-destroying enzyme, in different
polypeptide profile, in being unable to replicate at temperatures above 25
degrees C, and in host range.
Copyright © 1997, American Society for Microbiology
Characterization of infectious salmon anemia virus, an orthomyxo-like virus isolated from Atlantic salmon (Salmo salar L.)
National Veterinary Institute, Oslo, Norway. Knut.Falk@vetinst.sri.telemax.no
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